The line at the “Farewell to Arms Freedom” festival in the Denver suburb of Glendale stretched more than half a mile, the Denver Post reported. Magpul Industries, a maker of firearms accessories based in Erie, Colo., had donated 20,000 magazines for the event, with 1,500 given away and the rest to be sold at a discount.

The Post reported that the proceeds would go to the effort to recall two state senators who helped push through the law, which goes into effect Monday. The event was put on by Free Colorado, which says on its website that it is a nonprofit aimed at ensuring the rights of firearm owners.

The new law limits gun magazines to 15 rounds. People can still possess larger magazines, but those can’t be sold or transferred to other people in Colorado after Monday.

The law was passed in the wake of the shooting at Sandy Hook Elementary School in Connecticut, in which a gunman used 30-round magazines on a Bushmaster rifle to fire 154 bullets in less than five minutes. He killed 20 first-graders and six teachers and staff before shooting himself with a pistol.

"I don't see this as gun control," state Rep. Rhonda Fields, D-Aurora, who is not a target of the recall effort, told NBC station KUSA of Denver. “These are common sense measures to deal with gun violence. We're not taking away people's Second Amendment rights. People can still have access to guns."

But such arguments haven’t satisified opponents. Magpul has threatened to move out of Colorado over the ban.

"We are not going to take this lying down," said Kelly Maher, spokesperson for Free Colorado, told KUSA. "We are going to stand up and we are going to fight for what we believe in."